1. Field of the Invention
The present invention relates to a cable fixing device used for fixing a cable on electronic equipment.
2. Description Related to the Prior Art
Electronic equipment uses a cable to transmit various types of electric signals to peripheral equipment. Taking a measuring instrument as an example, the measuring instrument is connected to a control instrument through a cable in order to establish communication of a measurement command signal, a measurement signal, and the like between the measuring instrument and the control instrument.
The cable is composed of a plurality of central lines and a resin sheath (jacket) for protecting the central lines. Each central line is connected to a circuit board provided in the electronic equipment. This connection is often established by soldering. If the cable is pulled or twisted during the use of the electronic equipment, the tension or torsion is transmitted to the cable in the electronic equipment. Repetition of transmission of the tension or torsion causes fatigue of a solder joint of each central line, and brings about a break.
For the purpose of preventing the transmission of the tension or torsion of the cable to the inside of the electronic equipment, a cable fixing device is used to fix the cable on the electronic equipment. Japanese Utility Model Laid-Open Publication No. 62-135488 describes a cord fixing device in which a plurality of engaging plates is formed in parallel integrally on a cord, though it is not a cable, with a gap left between each two of the engaging plates. Each of the gaps and the engaging plates differs in size. Depending on the size of a slit formed in a frame of electric equipment (corresponding to the electronic equipment), an appropriate gap is chosen out of the plurality of gaps, and the chosen gap is engaged into the slit. Two of the parallel engaging plates are disposed in front of and behind the frame, to regulate back-and-forth movement of the cord. Thus, even if the cord is pulled or twisted, this movement is prevented from being transmitted to the cord in the electronic equipment. Note that the Japanese Utility Model Laid-Open Publication No. 62-135488 describes that a fixing board formed with a plurality of openings is used and the cord is drawn through each opening. This fixing board does not aim to eliminate the tension or torsion, but aims to straighten the cords for the purpose of preventing entwinement of the cords in the electronic equipment.
As an example of the electronic equipment, a load cell is known. The load cell measures a load of an object suspended thereon by converting the amount of strain into an electric signal. An obtained load signal is sent to a control instrument through a cable. The load cells use several types of cable fixing devices in order to protect a connection portion of the cable.
According to one type of the cable fixing devices, the cable is secured by a rubber sleeve formed with a flange at its distal end. The load cell is formed with a cable chamber in its cell body. This chamber is in the shape of a round tube and conical at its front end. The rubber sleeve is fitted onto the cable and then inserted into the chamber. Screwing a nut, which is fitted onto the rubber sleeve, into the chamber presses the flange against the conical portion. The pressed flange catches and secures the cable.
In addition to the use of the rubber sleeve, it is also known that a stopper is formed with an adhesive or a wire in the cell body for reinforcement. A partition that is formed with a small opening for drawing the cable therethrough is present between the cell body and the chamber. Focusing attention on this partition, the cable present inside of the partition is wound with the wire or secured to the partition with the adhesive, as the stopper.
Another type of the cable fixing devices is a pair of half clamps of an approximately half ring shape that catches the circumference of the cable to secure the cable. The pair of half clamps is inserted into the chamber in a state of being disposed onto the circumference of the cable. Then, a nut that is fitted onto the cable is screwed into the chamber. Since this nut presses the half clamps, the half clamps get near each other along the conical portion, and hence catch the circumference of the cable and secure the cable.
The cord fixing device according to the Japanese Utility Model Laid-Open Publication No. 62-135488 is available to a cable, but is not available to a general-purpose cable because the plurality of engaging plates is formed integrally with the cable. Also, since a pair of engaging plates is fitted into the slit of the plate-shaped frame, this cord fixing device cannot be used in electronic equipment that does not have a plate-shaped secure portion, and has limited applications.
The sheath of the cable is made of fluororesin inmost cases. The fluororesin are smooth and have a low coefficient of friction against rubber. Thus, the cable fixing device that secures the cable by using the rubber sleeve cannot securely fix the cable, and strongly pulling or twisting the cable moves the cable in the rubber sleeve. Furthermore, the enforcement with the wire or the adhesive is inferior in durability, because the adhesive deteriorates with use. There are also problems that the wire is vulnerable to torsion and needs time and effort at mounting.
According to the cable fixing device that secures the cable by the pair of half clamps, the half clamps dig into the cable. Thus, the cable is susceptible to damage and the central lines possibly break. Also, repetition of application of the tension or torsion to the cable chips or deforms the sheath. Since the half clamps are made of metal, not rubber, the fixation of the cable is loosened.